Generally, inductive power transfer systems have a number of advantages over conductive power transfer systems. E.g., for electric vehicles it means that a plugging of a cable is no longer required.
FIG. 1 shows a schematic diagram of an inductive power transfer system 100 as known in the art.
As shown in FIG. 1, an inductive power transfer system 100 comprises at a transmission side a DC/AC converter 102, a transmission side controller 104, a transmission side compensation capacitor 106, and a transmitter coil 108 connected in series to the transmission side compensation capacitor 106. The series connection of the transmission side compensation capacitor 106 and the transmitter coil 108 is connected to the output side of the DC/AC converter 104.
As shown in FIG. 1, the inductive power transfer system 100 comprises at a receiving side a receiver coil 110 connected in series to a receiving side compensation capacitor 112. The series connection of the receiver coil 110 and the receiving side compensation capacitor 112 is connected to an input side of an AC/DC converter 114 which is operated under control of a receiving side controller 116. Parallel to the series connection of the receiver coil 110 and the receiving side compensation capacitor 112 there is connected a short circuit protection switch 118. At the output of the AC/DC converter 114 there is connected a load 120. For the connection of the load 120 there may be provided a DC/DC converter for control of the power level delivered to the load 120 (not shown in FIG. 1).
As shown in FIG. 1, a wireless communication link 122 may be established from the receiving side to the transmission side for exchange of control data and/or measurement data between from the receiving side to the transmission side.
Operatively, the DC/AC converter 102 is adapted to receive a DC input signal and adapted to convert it into a transmission side AC signal. The transmission side AC signal is output to the series connection of the transmission side compensation capacitor 106 and the transmitter coil 108 for generation of an oscillating magnetic field. The transmission side controller 104 is adapted to measure the characteristics of the transmission side AC signal and optionally the DC input signal for control of the DC/AC converter 102. In more detail, the transmission side controller 104 is adapted to control the DC/AC converter 102 such that the generated magnetic field oscillates at resonant frequency of the series connection of the transmission side compensation capacitor 106 and the transmitter coil 108.
Operatively, the receiver coil 110, when placed in the magnetic field produced by the transmitter coil 108, receives energy transmitted by the transmitter coil 108 through inductive coupling. The inductive coupling leads to the generation of a receiving side AC signal. Under control of the transmission side controller 116 the AC/DC converter 114 is adapted to convert the receiving side AC signal into a load side DC signal which is then forwarded to the load 120.
Operatively, the receiving side controller 116 is adapted to measure the receiving side AC signal and optionally the load side DC signal for control of a power delivered to the load 120. Further, the receiving side controller 116 is adapted to detect an error state at the receiving side for actuation of the short circuit protection switch 118. Operatively, measurement data and control data may be sent over the wireless communication link 122 to improve the control and to inform the transmitting side on fault conditions at the receiving side.
Generally, in inductive power transfer systems there is no direct hardware connection between the transmission side and the receiving side. However, in cases of errors on the receiving side it is essential that a response to the error state is achieved as soon as possible to reduce or stop power transmission from the transmission side.
Further, if an open circuit error occurs at the receiving side, the receiving side AC signal will increase to levels that may be destructive to components in the inductive power transfer system or that may be even dangerous. Currently this problem is solved by detecting the over-voltage at the receiving side and by shorting the secondary resonant circuit constituted by the receiver coil 110 and the receiving side compensation capacitor 112 using the short circuit protection switch 118. Optionally, the error has to be communicated via the wireless communication link 122 to the transmission side to stop the power transmission. This short circuit protection switch 118 can be implemented using dedicated switches or, when available, using two high-side or two low-side active switches in the AC/DC converter 114.
However, communicating the error from the receiving side to the transmission side may be too slow. There are multiple delays added due to the analogue to digital conversion, the processing of the signal and the transmission delay caused by the wireless communication link 122.
Further, while the active short-circuiting by the short circuit protection switch 118 at the receiving side adds some level of safety it is nevertheless possible that the short circuit current increases above the rating of hardware components. Also, using the short circuit protection switch 118 leads to increased costs and complexity.